On Thu 17-10-19 16:21:09, Oscar Salvador wrote:
> From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>
> The call to get_user_pages_fast is only to get the pointer to a struct
> page of a given address, pinning it is memory-poisoning handler's job,
> so drop the refcount grabbed by get_user_pages_fast
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
> mm/madvise.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 2be9f3fdb05e..89ed9a22ff4f 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -878,16 +878,24 @@ static int madvise_inject_error(int behavior,
> */
> order = compound_order(compound_head(page));
>
> - if (PageHWPoison(page)) {
> - put_page(page);
> + /*
> + * The get_user_pages_fast() is just to get the pfn of the
> + * given address, and the refcount has nothing to do with
> + * what we try to test, so it should be released immediately.
> + * This is racy but it's intended because the real hardware
> + * errors could happen at any moment and memory error handlers
> + * must properly handle the race.
> + */
> + put_page(page);
> +
> + if (PageHWPoison(page))
> continue;
> - }
>
> if (behavior == MADV_SOFT_OFFLINE) {
> pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
> pfn, start);
>
> - ret = soft_offline_page(page, MF_COUNT_INCREASED);
> + ret = soft_offline_page(page, 0);
What does prevent this struct page to go away completely?
> if (ret)
> return ret;
> continue;
> @@ -895,14 +903,6 @@ static int madvise_inject_error(int behavior,
>
> pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
> pfn, start);
> -
> - /*
> - * Drop the page reference taken by get_user_pages_fast(). In
> - * the absence of MF_COUNT_INCREASED the memory_failure()
> - * routine is responsible for pinning the page to prevent it
> - * from being released back to the page allocator.
> - */
> - put_page(page);
> ret = memory_failure(pfn, 0);
> if (ret)
> return ret;
> --
> 2.12.3
>
--
Michal Hocko
SUSE Labs
